1. Field of the Invention
The present invention relates to a moving-object height determining apparatus which tracks and monitors a moving-object such as a human from a two-dimensional image captured from above by single image-capturing means to calculate a relative height of two moving-objects existing relatively close to each other.
2. Disclosure of the Prior Art
Conventionally, there is a technique for identifying a moving-object from a two-dimensional image. In this technique, a moving-object is extracted utilizing a concentration difference between the moving-object and a background with respect to a two-dimensional image in a monitor region captured by a video camera. As a technique for determining whether the extracted moving-object is a target moving-object to be monitored, if a subject to be monitored is a human, an object image of the extracted moving-object is directly or indirectly verified against a standard object image which is imitated from an outer shape of the human.
In order to precisely measure a human at the busy hour, there is a known stereo image measuring technique in which images of the same monitoring region are captured by two cameras to obtain a stereo image, a distance between a subject to be monitored and humans is measured based on a principle of triangulation from the stereo image, the humans are separated from each other, and the respective positions of the humans are recognized.
In the moving-object identifying technique, when the moving-object is to be extracted, not only the target moving-object which is the subject to be monitored, but also accessories of the moving-object are also extracted as the subject to be monitored in some cases. For example, if the subject to be monitored is a human, a shadow of the human, a large bag carried by the human, a hand truck moved by the human and the like could be extracted as the moving-object of the subject to be monitored. This is because that if the sensitivity of verification is made strict, there is an adverse possibility that a moving-object of a subject to be monitored can not be found, it is necessary to relax the verification sensitivity to some extent.
In this case, in the real space coordinate system, since all of a shadow of a human, a large bag carried by the human, a hand truck moved by the human and the like which are not the subject to be monitored are lower in height than the human who is the subject to be monitored, it is considered to determine the height of the moving-object extracted by the stereo image measuring technique to eliminate information which is not the subject to be monitored.
According to the stereo image measuring technique, however, the quantity of image data to be processed is increased. Therefore, the image processing speed becomes slow, a large capacity memory is required, and at least two cameras must be prepared as the image-capturing means. As a result, there arises a problem that the apparatus is increased in size and cost.